There has been conventionally promoted technical development of an ASV (Advanced Safety Vehicle) which gives warnings or operational support to a driver to secure safe driving of the vehicle. The ASV is especially required to detect a road boundary in order to prevent the vehicle from running off a road. Therefore, there has been often used a method of detecting traffic signs defining a roadway, such as traffic lanes and raised markers on the road surface, using a camera mounted on a vehicle.
However, though existence of the traffic signs can be expected in the case of an expressway or a properly improved road, there is often not a traffic sign outside a lane edge in the case of a narrow road or a road under improvement. Furthermore, in the case of a road with a short curve diameter, it is difficult to judge a road boundary because the lanes at a curved part of the road are difficult to be caught by a camera. Therefore, it is necessary to judge a road boundary not only from traffic signs such as lanes and raised markers but also from three-dimensional objects such as walkway/roadway separation blocks, a walkway, a hedge, a guardrail, a side wall and a pole.
As a method for detecting a road boundary demarcated by a three-dimensional object with a camera, there is a method using two or more cameras. For example, in Patent Literature 1, there is proposed a method in which a road boundary is detected by calculating the height of a three-dimensional object in an image capture area from the road surface on the basis of stereo images obtained by two cameras to detect a continuous three-dimensional object such as a guardrail and a side wall.
In Patent Literature 2, there is disclosed a road shoulder detection device and method using two cameras and adopting a plane projection stereo method. In the plane projection stereo method, all objects in an image obtained by one camera are assumed to exist on a road plane, and this image is transformed to an image viewed from the other camera. In the transformed image, a part corresponding to the road plane is not transformed, and only parts corresponding to three-dimensional objects are transformed. By comparing this transformed image and an image obtained by the other camera, the three-dimensional objects on the road plane can be detected.